Chromatin remodeling complexes are single- or multi-subunit protein complexes that are thought to regulate transcription by modifying the composition, occupancy, or positioning of nucleosomes along the genome. Many mutations in chromatin remodeling complex subunits are associated with intellectual disability and autism, suggesting that neurons may require strict chromatin regulation to establish neuronal connectivity. Therefore, understanding how chromatin remodeling regulates circuit development is crucial to discovering treatments for these neurodevelopmental disorders. Like many other chromatin remodeling complexes, mutations in subunits of the nucleosome remodeling and deacetylase (NuRD) complex are associated with intellectual disability and autism. Unique among chromatin remodeling complexes though, the NuRD complex is endowed with two enzymes: a chromatin remodeling ATPase and a histone deacetylase, through Chd3/4 and Hdac1/2, respectively. Previously, the Bonni laboratory discovered that Chd4 is required to establish connectivity of the cerebellar granule neuron into the circuit of the cerebellar cortex. Chd4 regulates both the elimination of dendrites and the formation of presynaptic boutons during granule neuron development. These observations raise vital questions about how NuRD complex function leads to granule neuron connectivity. Various scaffold subunits are thought to regulate the function of the complex, but only Mbd3 is required for complex assembly. Preliminary evidence suggests that Mbd3 controls transcription of a subset of Chd4- dependent genes in the cerebellum, potentially by regulating Chd4 function directly at these sites. To clarify how Mbd3 regulates neuronal connectivity, this proposal will define roles for Mbd3 in (1) granule neuron connectivity with in vivo electroporation and imaging approaches; and (2) Chd4-dependent transcription with chromatin immunoprecipitation (ChIP)-seq and bioinformatic analyses. Clarifying these mechanisms will develop fundamental insight into Mbd3?s role in NuRD complex function and brain development, illuminating potential mechanisms of neurodevelopmental disorder.